Lithium secondary battery and method of fabricating the same

ABSTRACT

A lithium secondary battery includes a cathode formed from a cathode active material including a first cathode active material particle and a second cathode active material particle, an anode and a separator interposed between the cathode and the anode. The first cathode active material particle includes a lithium metal oxide including a continuous concentration gradient in at least one region between a central portion and a surface portion. The second cathode active material particle includes a lithium metal oxide including at least two metals except for lithium which have constant concentrations from a central portion to a surface, and the second cathode active material particle includes an excess amount of nickel among the metals except for lithium.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Korean Patent Application Nos.10-2016-0154284 and 10-2017-0120353, filed Nov. 18, 2016 and Sep. 19,2017, respectively, the disclosures of which are hereby incorporated intheir entirety by reference herein.

BACKGROUND

1. Field

The present invention relates to a lithium secondary battery and amethod of fabricating the same. More particularly, the present inventionrelates to a lithium secondary battery including a lithium metal oxideand a method of fabricating the same.

2. Description of the Related Art

A secondary battery which can be charged and discharged repeatedly hasbeen widely employed as a power source of a mobile electronic devicesuch as a camcorder, a mobile phone, a laptop computer, etc., accordingto developments of information and display technologies. Recently, abattery pack including the secondary battery is being developed andapplied as a power source of an eco-friendly vehicle such as a hybridautomobile.

The secondary battery includes, e.g., a lithium secondary battery, anickel-cadmium battery, a nickel-hydrogen battery, etc. The lithiumsecondary battery is highlighted due to high operational voltage andenergy density per unit weight, a high charging rate, a compactdimension, etc.

For example, the lithium secondary battery may include an electrodeassembly including a cathode, an anode and a separation layer, and anelectrolyte immersing the electrode assembly. The lithium secondarybattery may further include an outer case having, e.g., a pouch shape.

A lithium metal oxide may be used as a cathode active material of thelithium secondary battery preferably having high capacity, power andlife-time. Further, a stability of the lithium secondary battery or thecathode active material under a harsh condition at a high temperature ora low temperature is also required as an industrial application of thelithium secondary battery is expanded. Additionally, when the lithiumsecondary battery or the cathode active material is penetrated by anexternal object, a resistance with respect to failures such as ashort-circuit, an ignition or an explosion may be also needed.

However, the cathode active material having all of the above-mentionedproperties may not be easily achieved. For example, Korean Publicationof Patent Application No. 10-2017-0093085 discloses a cathode activematerial including a transition metal compound and an ion adsorbingbinder which may not have sufficient life-time and stability.

SUMMARY

According to an aspect of the present invention, there is provided alithium secondary battery having improved electrical and mechanicalreliability and stability.

According to an aspect of the present invention, there is provided amethod of fabricating a lithium secondary battery having improvedelectrical and mechanical reliability and stability.

According to example embodiments, a lithium secondary battery comprisesa cathode formed from a cathode active material including a firstcathode active material particle and a second cathode active materialparticle, an anode, and a separator interposed between the cathode andthe anode. The first cathode active material particle includes a lithiummetal oxide including a continuous concentration gradient in at leastone region between a central portion and a surface portion. The secondcathode active material particle includes a lithium metal oxideincluding at least two metals except for lithium which have constantconcentrations from a central portion to a surface, and the secondcathode active material particle includes an excess amount of nickelamong the metals except for lithium.

In some embodiments, the first cathode active material particle may afirst metal having a continuously decreasing concentration between thecentral portion and the surface portion, and a second metal having acontinuously increasing concentration between the central portion andthe surface portion.

In some embodiments, the first cathode active material particle mayfurther include a third metal having a constant concentration from thecentral portion to the surface portion.

In some embodiments, the first cathode active material particle may berepresented by the following Chemical Formula 1.Li_(x)M1_(a)M2_(b)M3_(c)O_(y)   [Chemical Formula 1]

In the Chemical Formula 1 above, M1, M2 and M3 may each represent thefirst metal, the second metal and the third metal, and may be selectedfrom Ni, Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb,Mo, Al, Ga or B, and 0<x≤1.1, 2≤y≤2.02, 0<a<1, 0<b<1, 0<c<1, and0<a+b+c≤1.

In some embodiments, 0.6≤a≤0.95 and 0.05≤b+c≤0.4 in the Chemical Formula1.

In some embodiments, 0.7≤a≤0.9 and 0.1≤b+c≤0.3 in the Chemical Formula1.

In some embodiments, the first metal may be nickel (Ni), the secondmetal may be manganese (Mn) and the third metal may be cobalt (Co).

In some embodiments, the first cathode active material particle mayinclude a concentration gradient layer formed between the centralportion and the surface portion.

In some embodiments, the concentration gradient layer may include acontinuous concentration gradient. The central portion and the surfaceportion may each have a constant concentration composition, and thecentral portion and the surface portion may have different concentrationcompositions from each other through the concentration gradient layer.

In some embodiments, the first cathode active material particle may havethe continuous concentration gradient throughout an entire region fromthe central portion to a surface thereof.

In some embodiments, the second cathode active material particle may berepresented by the following Chemical Formula 2.Li_(x)M1′_(a)M2′_(b)M3′_(c)O_(y)   [Chemical Formula 2]

In the Chemical Formula 2 above, M1′ may be nickel, and M2′ and M3′ maybe selected from Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba,Zr, Nb, Mo, Al, Ga, W or B, and 0<x≤1.1, 2≤y≤2.02, 0<a+b+c≤1,0.48≤a≤0.52 0.18≤b≤0.22 and 0.28≤c≤0.32.

In some embodiments, 0.49≤a≤0.51, 0.19≤b≤0.21 and 0.29≤c≤0.31 in theChemical Formula 2.

In some embodiments, M2′ and M3′ may be cobalt (Co) and manganese (Mn),respectively.

In some embodiments, a molar ratio of nickel, cobalt and manganese inthe second cathode active material particle may be 5:2:3.

In some embodiments, a blending ratio of the first cathode activematerial particle and the second cathode active material particle may bein a range from 7:3 to 1:9.

In some embodiments, a blending ratio of the first cathode activematerial particle and the second cathode active material particle may bein a range from 5:5 to 1:9.

In some embodiments, an average diameter (D₅₀) of the second cathodeactive material particle may be in a range from 3 μm to 15 μm.

In some embodiments, an average diameter (D₅₀) of the second cathodeactive material particle may be in a range from 4.5 μm to 15 μm.

According to example embodiments as described above, a cathode activematerial of a lithium secondary battery may include a first cathodeactive material particle having a concentration gradient, and a secondcathode active material particle having a fixed concentration profile.High capacity and power of the lithium secondary battery may be realizedby the first cathode active material particle, and penetration stabilityand thermal stability of the lithium secondary battery may be obtainedby the second cathode active material particle.

Therefore, both electrical performance and mechanical stability of thelithium secondary battery may be improved.

In example embodiments, the first and second cathode active materialparticles may include lithium metal oxides containing nickel, and thesecond cathode active material particle may have a concentration ofnickel less than that of the first cathode active material particle.Accordingly, life-time and penetration stability of the lithiumsecondary battery may be further improved through a combination with theconcentration gradient of the first cathode active material particle.

In some embodiments, a size of the second cathode active materialparticle may be controlled, or a coating layer may be formed on thefirst cathode active material particle so that life-time and penetrationstability of the lithium secondary battery may be further improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating a lithiumsecondary battery in accordance with example embodiments;

FIG. 2A is a schematic cross-sectional view illustrating positions atwhich a concentration gradient of a first cathode active materialparticle prepared in accordance with some example embodiments ismeasured;

FIG. 2B is a schematic view illustrating positions at which aconcentration gradient of a first cathode active material particleprepared in accordance with some example embodiments is measured;

FIG. 3 is a schematic cross-sectional view illustrating positions atwhich a concentration gradient of a first cathode active materialparticle prepared in accordance with some example embodiments ismeasured;

FIG. 4 is a cross-sectional image of a first cathode active materialparticle prepared in accordance with example embodiments; and

FIG. 5 is a cross-sectional image of a lithium metal oxide used inComparative Examples.

DETAILED DESCRIPTION OF THE EMBODIMENTS

According to example embodiments of the present invention, a lithiumsecondary battery having improved electrical performance and mechanicalstability is provided. The lithium secondary battery may include acathode active material including a first cathode active materialparticle having a concentration gradient, and a second cathode activematerial particle having a fixed concentration profile. According toexample embodiments, a method of manufacturing the lithium secondarybattery or the cathode active material is also provided.

Hereinafter, the present invention will be described in detail withreference to the accompanying drawings. However, those skilled in theart will appreciate that such embodiments described with reference tothe accompanying drawings are provided to further understand the spiritof the present invention and do not limit subject matters to beprotected as disclosed in the detailed description and appended claims.

The terms “a first” and “a second” used herein are not intended tospecify the number or the order of objects, and only used to identifydifferent elements or objects.

FIG. 1 is a schematic cross-sectional view illustrating a lithiumsecondary battery in accordance with example embodiments.

Referring to FIG. 1, a lithium secondary battery may include a cathode130, and anode 140 and a separation layer interposed between the cathode130 and the anode 140.

The cathode may include a cathode current collector 110 and a cathodeactive material layer 115 formed by coating a cathode active material onthe cathode current collector 110. In example embodiments, the cathodeactive material may include a first cathode active material particle anda second cathode active material particle.

The first cathode active material particle may include a lithium metaloxide having a continuous concentration gradient from a central portionof the particle to a surface of the particle. In some embodiments, thefirst cathode active material particle may have a full concentrationgradient (FCG) structure in which the concentration gradient may besubstantially formed throughout the entire particle.

In some embodiments, the first cathode active material particle mayinclude a lithium metal oxide, at least one region of which may have acontinuous concentration gradient between a central portion and asurface portion. For example, the first cathode active material particlemay include a concentration gradient layer formed between the centralportion and the surface portion.

In some embodiments, each concentration of lithium and oxygen may besubstantially fixed throughout an entire region of the particle, and atleast one element except for lithium and oxygen may have the continuousconcentration gradient.

The term “continuous concentration gradient” used herein may indicate aconcentration profile which may be changed with a uniform trend ortendency between the central portion and the surface portion. Theuniform trend may include an increasing trend or a decreasing trend.

The term “central portion” used herein may include a central point ofthe active material particle and may also include a region within apredetermined diameter from the central point. For example, “centralportion” may encompass a region within a diameter of about 0.2 μm orabout 0.1 μm from the central point of the active material particle.

The term “surface portion” used herein may include an outermost surfaceof the active material particle, and may also include a predeterminedthickness from the outermost surface. For example, “surface portion” mayinclude a region within a thickness of about 0.2 μm or about 0.1 μm fromthe outermost surface of the active material particle.

In some embodiments, the continuous concentration particle may include alinear concentration profile or a curved concentration profile. In thecurved concentration profile, the concentration may change in a uniformtrend without any inflection point.

In an embodiment, at least one metal except for lithium included in thefirst cathode active material particle may have an increasing continuousconcentration gradient, and at least one metal except for lithiumincluded in the first cathode active material particle may have andecreasing continuous concentration gradient

In an embodiment, at least one metal included in the first cathodeactive material particle except for lithium may have a substantiallyconstant concentration from the central portion to the surface.

In example embodiments, the first cathode active material particle mayinclude a nickel-containing lithium metal oxide, and nickel may have acontinuous concentration gradient throughout an entire region of theparticle or in a specific region between the central portion and thesurface portion. In example embodiments, a concentration (or a molarratio) of nickel may be continuously decreased between the centralportion and the surface portion in the first cathode active materialparticle.

In an embodiment, metals included in the first cathode active materialparticle except for lithium may include a first metal M1 and a secondmetal M2. The first metal M1 may have a continuously decreasingconcentration gradient from the central portion to the surface. Thesecond metal M2 have a continuously increasing concentration gradientfrom the central portion to the surface.

In an embodiment, the metals included in the first cathode activematerial particle except for lithium may further include a third metalM3. The third metal M3 may have a substantially constant concentrationfrom the central portion to the surface.

The term “concentration” used herein may indicate, e.g., a molar ratioof the first to third metals.

For example, the first cathode active material particle may berepresented by the following Chemical Formula 1.Li_(x)M1_(a)M2_(b)M3_(c)O_(y)   [Chemical Formula 1]

In the Chemical Formula 1 above, M1, M2 and M3 may be selected from Ni,Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al,Ga and B, and 0<x≤1.1, 2≤y≤2.02, 0<a<1, 0<b<1, 0<c<1, and 0<a+b+c≤1.

In some embodiments, M1, M2 and M3 of Chemical Formula 1 may be nickel(Ni), manganese (Mn) and cobalt (Co), respectively.

For example, nickel may serve as a metal related to a capacity of thelithium secondary battery. As an amount of nickel becomes higher,capacity and power of the lithium secondary battery may be improved.However, an excessive amount of nickel may degrade of a life-timeproperty of the battery, and may be disadvantageous in an aspect ofmechanical and electrical stability of the battery. For example, whenthe amount of nickel is excessively increased, defects such as ignitionor short-circuit by a penetration of an external object may not besufficiently suppressed.

However, according to example embodiments, nickel may be included as thefirst metal M1. Thus, the amount of nickel at the central portion may berelatively high to improve the capacity and power of the lithiumsecondary battery, and a concentration of nickel may be decreased fromthe central portion to the surface to prevent the defects from thepenetration and a life-time reduction.

For example, manganese (Mn) may serve as a metal related to themechanical and electrical stability of the lithium secondary battery. Inexample embodiments, an amount of Mn may be increased from the centralportion to the surface so that the defects from the penetration such asignition or short-circuit through the surface may be suppressed orreduced, and the life-time of the lithium secondary battery may be alsoenhanced.

For example, cobalt (Co) may serve as a metal related to a conductivityor a resistance of the lithium secondary battery. In exampleembodiments, a concentration of cobalt may be fixed or uniformlymaintained through an entire region of the first cathode active materialparticle. Thus, a current or a charge flow through the first cathodeactive material particle may be uniformly maintained while improving theconductivity of the battery and maintaining low resistance.

In some embodiments, in Chemical Formula 1, the first metal M1 may benickel, and, e.g., 0.6≤a≤0.95 and 0.05≤b+c≤0.4. For example, aconcentration (or a molar ratio) of nickel may be continuously decreasedfrom about 0.95 to about 0.6. In an embodiment, a concentration gradientlayer having a concentration gradient region may be formed between thecentral portion and the surface portion, and the concentration (or themolar ratio) of nickel may be continuously decreased from about 0.95 toabout 0.6 in the concentration gradient layer.

If a lower limit of the nickel concentration (e.g., a surfaceconcentration) is less than about 0.6, capacity and power at the surfaceof the first cathode active material particle may be excessivelydeteriorated. If an upper limit of the nickel concentration (e.g., acentral concentration) exceeds about 0.95, life-time and mechanicalstability at the central portion may be excessively degraded.

Preferably, in Chemical Formula 1, 0.7≤a≤0.9 and 0.1≤b+c≤0.3. In thiscase, both capacity and stability of the battery may be enhanced. In anembodiment, 0.77≤a≤0.83, 0.07≤b≤0.13 and 0.07≤c≤0.13, preferably0.79≤a≤0.81, 0.09≤b≤0.11 and 0.09≤c≤0.11.

According to example embodiments as described above, the first cathodeactive material particle may include the continuous concentrationgradient between the central portion and the surface.

In some embodiments, the first cathode active material particle may havea FCG structure including the concentration gradient at substantially anentire region thereof. In this case, for example, a concentration of Nimay be continuously decreased from the central portion to the surface,and a concentration of Mn may be continuously increased from the centralportion to the surface. A concentration of Co may be substantiallyconstant from the central portion to the surface.

In some embodiments, the first cathode active material particle mayinclude the concentration gradient layer at a specific region betweenthe surface portion and the surface portion. In the concentrationgradient layer, a concentration of Ni may be continuously decreased, aconcentration of Mn may be continuously increased, and a concentrationof Co may be substantially constant.

In this case, elements of the first cathode active material particle mayhave uniform compositions at the central portion and the surfaceportion. For example, the concentrations of Ni and Mn may be constant ateach of the central portion and the surface portion. The concentrationof Ni may become relatively high at the central portion, and theconcentration of Mn may become relatively high at the surface portionthrough the concentration gradient layer. The concentration of Co may besubstantially uniform or constant throughout the central portion, theconcentration gradient layer and the surface portion.

In some embodiments, the first cathode active material particle mayfurther include a coating layer on the surface thereof. For example, thecoating layer may include Al, Ti, Ba, Zr, Si, B, Mg, P, an alloy thereofor on oxide thereof. These may be used alone or in a mixture thereof.The first cathode active material particle may be passivated by thecoating layer so that penetration stability and life-time of the batterymay be further improved.

In an embodiment, the elements, the alloy or the oxide of the coatinglayer may be inserted in the first cathode active material particle asdopants.

In some embodiments, the first cathode active material particle may beformed from a primary particle having a rod-type shape. An averagediameter of the first cathode active material particle may be in a rangefrom about 3 μm to about 25 μm.

The cathode active material may include a second cathode active materialparticle blended with the first cathode active material particle. Inexample embodiments, the second cathode active material particle mayhave a substantially constant or fixed concentration throughout anentire region of the particle.

The second cathode active material particle may include a lithium metaloxide. In example embodiments, the second cathode active materialparticle may include a nickel-containing lithium metal oxide. In thesecond cathode active material particle, a concentration of nickel maybe less than that in the first cathode active material particle. In anembodiment, the concentration of nickel in the second cathode activematerial particle may be fixed to be less than the concentration ofnickel at the surface of the first cathode active material particle.

In some embodiments, the second cathode active material particle mayinclude at least two metals except for lithium. Concentrations of themetals except for lithium may be maintained constant from a centralportion of the particle to a surface of the particle.

In some embodiments, the second cathode active material particle mayinclude a first metal M1′, a second metal M2′ and a third metal M3′. Forexample, the first metal M1′, the second metal M2′ and the third metalM3′ may be nickel (Ni), cobalt (Co) and manganese (Mn), respectively.

As described above, concentrations or molar ratios of Ni, Co and Mn maybe uniform or constant throughout the entire region of the secondcathode active material particle. In some embodiments, the secondcathode active material particle may include an excess amount of nickel,and the concentrations of nickel, manganese and cobalt may becomesequentially smaller in consideration of both capacity and stability ofthe lithium secondary battery. In example embodiments, the concentrationratio of Ni:Co:Mn in the second cathode active material particle may besubstantially 5:2:3.

The term “excess amount” used herein may indicate that the metal elementof the excess amount has the largest concentration or molar ratio amongthe metal elements except for lithium in the cathode active materialparticle.

For example, the second cathode active material particle may berepresented by the following Chemical Formula 2.Li_(x)M1′_(a)M2′_(b)M3′_(c)O_(y)   [Chemical Formula 2]

In the Chemical Formula 2 above, M1′, M2′ and M3′ may be selected fromNi, Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo,Al, Ga, W and B, and 0<x≤1.1, 2≤y≤2.02 and 0<a+b+c≤1.

In some embodiments, in the Chemical Formula 2 above, 0.48≤a≤0.520.18≤b≤0.22 and 0.28≤c≤0.32, preferably, 0.49≤a≤0.51, 0.19≤b≤0.21 and0.29≤c≤0.31.

In some embodiments, as described above, the first metal M1′, the secondmetal M2′ and the third metal M3′ may be Ni, Co and Mn, respectively.

In example embodiments, a thermal stability of the lithium secondarybattery or the cathode may be enhanced through blending the secondcathode active material particle with the first cathode active materialparticle. The second cathode active material particle may have a nickelconcentration or a nickel molar ratio less than that of the firstcathode active material particle through an entire region of theparticle, and Mn may be distributed uniformly throughout the secondcathode active material particle.

Thus, the ignition or explosion occurring by the penetration of theexternal object may be avoided, and a heat resistance may be alsoimproved during repeated charging and discharging so that an operationaluniformity and the life-time of the lithium secondary battery may beremarkably improved.

Further, a cobalt concentration may be constant through the entireregion of the second cathode active material particle so thatconductivity and resistance of the entire cathode may be uniformlymaintained.

In some embodiments, the concentration of nickel may be greater thanother metals (e.g., manganese and cobalt) in the second cathode activematerial particle, and the concentration of nickel in the second cathodeactive material particle may be less than the concentration of nickel inthe first cathode active material particle. Thus, a capacity reductiondue to an inclusion of the second cathode active material particle maybe suppressed while improving the life-time and penetration stability ofthe lithium secondary battery.

In some embodiments, an average diameter (D₅₀) of the second cathodeactive material particle may be in a range from about 3 μm to about 15μm. Within the above range, life-time and stability of the lithiumsecondary battery or the cathode may be improved without interfering inan electrical activity of the first cathode active material particle bythe second cathode active material particle. Preferably, the averagediameter (D₅₀) of the second cathode active material particle may be ina range from about 4.5 μm to about 15 μm

If the average diameter (D₅₀) of the second cathode active materialparticle is less than about 3 μm, a dimension of the particle may beexcessively decreased, and desired composition, activity and stabilitymay not be realized and controlled. If the average diameter (D₅₀) of thesecond cathode active material particle exceeds about 15 μm, anexcessive amount of heat may be required for a particle formation todegrade process efficiency.

In example embodiments, a mixing ratio of the first cathode activematerial particle and the second cathode active material particle maybe, e.g., in a range from 7:3 to 1:9, preferably, from 5:5 to 1:9.Within the above range, a thermal stability improvement and a preventionof a penetration-induced ignition by the second cathode active materialparticle may be more effectively achieved.

The first and second cathode active material particles may beindividually prepared, and then blended to obtain the cathode activematerial.

In a formation of the first cathode active material, metal precursorsolutions having different concentrations may be prepared. The metalprecursor solutions may include precursors of metals that may beincluded in the cathode active material. For example, the metalprecursors may include halides, hydroxides, acid salts, etc., of themetals.

For example, the metal precursors may include a lithium precursor (e.g.,a lithium oxide), a nickel precursor, a manganese precursor and a cobaltprecursor.

In example embodiments, a first precursor solution having a targetcomposition at the central portion (e.g., concentrations of nickel,manganese and cobalt at the central portion) and a second precursorsolution having a target composition at the surface or the surfaceportion (e.g., concentrations of nickel, manganese and cobalt at thesurface) may be each prepared.

Subsequently, the first and second precursor solution may be mixed and aprecipitate may be formed by a co-precipitation method. In someembodiments, a mixing ratio may be continuously changed so that acontinuous concentration gradient may be formed from the targetcomposition at the central portion to the target composition at thesurface. In some embodiments, the mixing ratio may be changed at aspecific period so that a concentration gradient layer may be formedbetween the central portion and the surface portion. Accordingly, theprecipitate may include a concentration gradient of the metals therein.

In some embodiments, a chelate agent and a basic agent (e.g., analkaline agent) may be added while forming the precipitate. In someembodiments, the precipitate may be thermally treated, and then alithium salt may be mixed and thermally treated again.

The second cathode active material particle may be formed by aprecipitation method using a metal precursor solution having a singletarget composition.

In example embodiments, the first cathode active material particle andthe second cathode active material particle may be blended to form thecathode active material. The cathode active material may be mixed andstirred together with a binder, a conductive additive and/or adispersive additive in a solvent to form a slurry. The slurry may becoated on the cathode current collector 110, and pressed and dried toobtain the cathode 130.

The cathode current collector 110 may include stainless-steel, nickel,aluminum, titanium, copper or an alloy thereof. Preferably, aluminum oran alloy thereof may be used.

The binder may include an organic based binder such as a polyvinylidenefluoride-hexafluoropropylene copolymer (PVDF-co-HFP),polyvinylidenefluoride (PVDF), polyacrylonitrile,polymethylmethacrylate, etc., or an aqueous based binder such asstyrene-butadiene rubber (SBR) that may be used with a thickener such ascarboxymethyl cellulose (CMC).

For example, a PVDF-based binder may be used as a cathode binder. Inthis case, an amount of the binder for forming the cathode activematerial layer 115, and an amount of the first and second cathode activematerial particles may be relatively increased. Thus, capacity and powerof the lithium secondary battery may be further improved.

The conductive additive may be added to facilitate an electron mobilitybetween the active material particles. For example, the conductiveadditive may include a carbon-based material such as graphite, carbonblack, graphene, carbon nanotube, etc., and/or a metal-based materialsuch as tin, tin oxide, titanium oxide, a perovskite material such asLaSrCoO₃ or LaSrMnO₃.

In example embodiments, an electrode density of the cathode 130 may bein a range from about 3.0 g/cc to about 3.9 g/cc, preferably, from 3.2g/cc to about 3.8 g/cc.

In example embodiments, the anode 140 may include an anode currentcollector 120 and an anode active material layer 125 formed by coatingan anode active material on the anode current collector 120.

The anode active material may include a material that may be capable ofadsorbing and ejecting lithium ions. For example, a carbon-basedmaterial such as a crystalline carbon, an amorphous carbon, a carboncomplex or a carbon fiber, a lithium alloy, silicon, tin, etc., may beused. The amorphous carbon may include a hard carbon, cokes, amesocarbon microbead (MCMB) calcinated at a temperature of 1,500 ° C. orless, a mesophase pitch-based carbon fiber (MPCF), ETC. The crystallinecarbon may include a graphite-based material, such as natural graphite,graphitized cokes, graphitized MCMB, graphitized MPCF, etc. The lithiumalloy may further include aluminum, zinc, bismuth, cadmium, antimony,silicon, lead, tin, gallium, or indium.

The anode current collector 120 may include gold, stainless-steel,nickel, aluminum, titanium, copper or an alloy thereof, preferably, mayinclude copper or a copper alloy.

In some embodiments, the anode active material may be mixed and stirredtogether with a binder, a conductive additive and/or a dispersiveadditive in a solvent to form a slurry. The slurry may be coated on theanode current collector 120, and pressed and dried to obtain the anode140.

The binder and the conductive additive substantially the same as orsimilar to those as mentioned above may be used. In some embodiments,the binder for the anode 140 may include an aqueous binder such as suchas styrene-butadiene rubber (SBR) that may be used with a thickener suchas carboxymethyl cellulose (CMC) so that compatibility with thecarbon-based active material may be improved.

A separator 150 may be interposed between the cathode 130 and the anode140. The separator 150 may include a porous polymer film prepared from,e.g., a polyolefin-based polymer such as an ethylene homopolymer, apropylene homopolymer, an ethylene/butene copolymer, an ethylene/hexenecopolymer, an ethylene/methacrylate copolymer, or the like. Theseparator 150 may be also formed from a non-woven fabric including aglass fiber with a high melting point, a polyethylene terephthalatefiber, or the like.

In some embodiments, an area and/or a volume of the anode 140 (e.g., acontact area with the separator 150) may be greater than that of thecathode 130. Thus, lithium ions generated from the cathode 130 may beeasily transferred to the anode 140 without loss by, e.g., precipitationor sedimentation. Therefore, the enhancement of power and stability bythe combination of the first and second cathode active materialparticles may be effectively implemented.

In example embodiments, an electrode cell 160 may be defined by thecathode 130, the anode 140 and the separator 150, and a plurality of theelectrode cells 160 may be stacked to form an electrode assembly having,e.g., a jelly roll shape. For example, the electrode assembly may beformed by winding, laminating or folding of the separator 150.

The electrode assembly may be accommodated in an external case 170together with an electrolyte to form the lithium secondary battery. Inexample embodiments, the electrolyte may include a non-aqueouselectrolyte solution.

The non-aqueous electrolyte solution may include a lithium salt and anorganic solvent. The lithium salt may be represented by Li⁺X⁻, and ananion of the lithium salt X⁻ may include, e.g., F⁻, Cl⁻, BP⁻, I⁻, NO₃ ⁻,N(CN)₂ ⁻, BF₄ ⁻, ClO₄ ⁻, PF₆ ⁻, (CF₃)₂PF₄ ⁻, (CF₃)₃PF₃ ⁻, (CF₃)₄PF₂ ⁻,(CF₃)₅PF⁻, (CF₃)₆P⁻, CF₃SO₃ ⁻, CF₃CF₂SO₃ ⁻, (CF₃SO₂)₂N , (FSO₂)₂N⁻,CF₃CF₂(CF₃)₂CO⁻, (CF₃SO₂)₂CH⁻, (SF₅)₃C⁻, (CF₃SO₂)₃C⁻, CF₃(CF₂)₇SO₃ ⁻,CF₃CO₂ ⁻, CH₃CO₂ ⁻, SCN⁻, (CF₃CF₂SO₂)₂N⁻, etc.

The organic solvent may include propylene carbonate (PC), ethylenecarbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC),ethylmethyl carbonate (EMC), methylpropyl carbonate, dipropyl carbonate,dimethyl sulfoxide, acetonitrile, dimethoxy ethane, diethoxy ethane,vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite,tetrahydrofuran, etc. These may be used alone or in a combinationthereof.

An electrode tab may be formed from each of the cathode currentcollector 110 and the anode current collector 120 to extend to one endof the external case 170. The electrode tabs may be welded together withthe one end of the external case 170 to form an electrode lead exposedat an outside of the external case 170.

The lithium secondary battery may be fabricated into a cylindrical shapeusing a can, a prismatic shape, a pouch shape, a coin shape, etc.

Hereinafter, preferred embodiments are proposed to more concretelydescribe the present invention. However, the following examples are onlygiven for illustrating the present invention and those skilled in therelated art will obviously understand that various alterations andmodifications are possible within the scope and spirit of the presentinvention. Such alterations and modifications are duly included in theappended claims.

Experimental Example 1: Blending a first cathode active materialincluding a concentration gradient layer in the middle of a particle anda second cathode active material having a fixed concentration

Fabrication of Lithium Secondary Battery

(1) Cathode

FIGS. 2A and 2B are schematic views illustrating positions at which aconcentration gradient of a first cathode active material particleprepared in accordance with some example embodiments is measured.

The first cathode active material particle having a concentrationgradient layer formed between a central portion and a surface portionwas prepared as follows.

A lithium metal oxide (CAM10a) was used as the first cathode activematerial (a first lithium metal oxide). A total composition of the firstlithium metal oxide was Li_(1.0)Ni_(0.80)Co_(0.11)Mn_(0.09)O₂, acomposition at the central portion (positions numerated from 1 to 12 inTable 1 below) was Li_(1.0)Ni_(0.802)Co_(0.11)Mn_(0.088)O₂, and acomposition at the surface portion (positions numerated from 12-5 to 13in Table 1 below) was Li_(1.0)Ni_(0.77)Co_(0.11)Mn_(0.12)O₂. Theconcentration gradient layer was formed between the central portion andthe surface portion (positions numerated from 12 to 12-4) to have aconcentration gradient of nickel and manganese therein.

Specifically, the concentration gradient of the first lithium metaloxide was formed as represented by Table 1 below (the concentration wasmeasured at positions from the central portion to the surface of thefirst lithium metal oxide), and the position of the concentrationgradient layer and the positions at which the concentrations weremeasured are illustrated in FIG. 2B.

In the first lithium metal oxide particle having a distance of 4.8 μmfrom a center and the surface, a molar ratio of each meal included inthe first lithium metal oxide particle was measured at positionsnumbered from 1 to 12 per a distance of 0.4 μm from the center. Themolar ratio of each metal was measured per a distance 0.04 μm (40 nm) atpositions numbered 12-1, 12-2, 12-3, 12-4, 12-5, 12-6, 12-7, 12-8 and12-9 between the positions numbered 12 and 13.

A second lithium metal oxide having a fixed total composition ofLi_(1.0)Ni_(1/2)Co_(1/5)Mn_(3/10)O₂ (NCM523) was used as the secondcathode active material particle. Blending ratios of the first lithiummetal oxide and the second lithium metal oxide were adjusted as listedin following Tables to form cathode active materials.

Denka Black was used as a conductive additive, and PVDF was used as abinder. The cathode active material, the conductive additive and thebinder were mixed by a weight ratio of 92:5:3 to form a positiveelectrode slurry. The positive electrode slurry was coated, dried, andpressed on an aluminum substrate to form a cathode. A density of thecathode after the pressing was 3.3 g/cc.

TABLE 1 Position Molar Ratio Molar Ratio Molar Ratio Number of Ni of Coof Mn 1 0.802 0.110 0.088 2 0.801 0.111 0.088 3 0.802 0.110 0.088 40.802 0.110 0.088 5 0.803 0.111 0.086 6 0.802 0.110 0.088 7 0.802 0.1100.088 8 0.802 0.109 0.089 9 0.801 0.110 0.089 10  0.802 0.110 0.088 11 0.802 0.108 0.090 12  0.800 0.110 0.090 12-1 0.794 0.110 0.096 12-20.789 0.109 0.102 12-3 0.782 0.110 0.108 12-4 0.777 0.110 0.113 12-50.770 0.110 0.120 12-6 0.771 0.110 0.119 12-7 0.770 0.110 0.120 12-80.769 0.111 0.120 12-9 0.770 0.109 0.121 13  0.770 0.110 0.120

(2) Anode

An anode slurry was prepared by mixing 93 wt % of a natural graphite asan anode active material, 5 wt % of a flake type conductive additiveKS6, 1 wt % of SBR as a binder, and 1 wt % of CMC as a thickener. Theanode slurry was coated, dried, and pressed on a copper substrate toform an anode.

(3) Lithium Secondary Battery

The cathode and the anode obtained as described above were notched witha proper size and stacked, and a separator (polyethylene, thickness: 25μm) was interposed between the cathode and the anode to form anelectrode cell. Each tab portion of the cathode and the anode waswelded. The welded cathode/separator/anode assembly was inserted in apouch, and three sides of the pouch (e.g., except for an electrolyteinjection side) were sealed. The tab portions were also included insealed portions. An electrolyte was injected through the electrolyteinjection side, and then the electrolyte injection side was also sealed.Subsequently, the above structure was impregnated for more than 12hours.

The electrolyte was prepared by dissolving 1M LiPF6 in a mixed solventof EC/EMC/DEC (25/45/30; volume ratio), and then 1 wt % of vinylenecarbonate, 0.5 wt % of 1,3-propensultone (PRS), and 0.5 wt % of lithiumbis (oxalato) borate (LiBOB) were added.

The lithium secondary battery as fabricated above was pre-charged byapplying a pre-charging current (2.5 A) corresponding to 0.25 C for 36minutes. After 1 hour, the battery was degased, aged for more than 24hours, and then a formation charging-discharging (charging condition ofCC-CV 0.2 C 4.2 V 0.05 C CUT-OFF, discharging condition CC 0.2 C 2.5 VCUT-OFF) was performed. Then, a standard charging-discharging (chargingcondition of CC-CV 0.5 C 4.2 V 0.05 C CUT-OFF, discharging condition CC0.5 C 2.5 V CUT-OFF) was performed.

Examples and Comparative Examples

Blends of the cathode active material particles CAM10a and NCM523 wereused in Examples. LiNi_(0.8)Co_(0.1)Mn_(0.1)O₂ (hereinafter, referred toas CAM20 and see an image of FIG. 5) having a uniform compositionthroughout an entire region of the particle was used as the cathodeactive material in Comparative Examples.

Methods of forming the cathode, the anode and the lithium secondarybattery were the same in Examples and Comparative Examples except forthe cathode active material particles.

(1-1) Experimental Example 1-1: Evaluation of life-time and penetrationstability depending on blending ratios of NCM523 (D50: 3 μm)

The battery cells prepared as described in Table 2 below were repeatedlycharged (CC-CV 2.0 C 4.2 V 0.05 C CUT-OFF) and discharged (CC 2.0 C 2.75V CUT-OFF) 500 times, and then a discharging capacity at a 500th cyclewas calculated as a percentage (%) with respect to a first cycledischarging capacity to measure the life-time property at a roomtemperature.

Additionally, the battery cells of Example and Comparative Examples werecharged (1C 4.2V 0.1C CUT-OFF), and then the battery cells werepenetrated by a nail having a diameter of 3 mm at a speed of 80 mm/secto check whether ignition or explosion occurred (O: Ignition orexplosion occurred, X: No ignition or explosion).

The results are shown in Table 2 below.

TABLE 2 Second Lithium Metal Oxide (D₅₀: 3 μm) Life-Time BlendingProperty First Lithium Ratio (500 cycle) Penetration Metal Oxide (wt %)(%) Stability Example 1-1-1 CAM10a 10 82 ◯ Example 1-1-2 CAM10a 20 82.5◯ Example 1-1-3 CAM10a 30 83.6 ◯ Example 1-1-4 CAM10a 40 84.6 ◯ Example1-1-5 CAM10a 50 85.7 X Example 1-1-6 CAM10a 60 86.2 X Example 1-1-7CAM10a 70 87.4 X Example 1-1-8 CAM10a 80 88.3 X Example 1-1-9 CAM10a 9089.3 X Comparative CAM20 0 69.8 ◯ Example 1-1-1 Comparative CAM20 1070.5 ◯ Example 1-1-2 Comparative CAM20 20 70.7 ◯ Example 1-1-3Comparative CAM20 30 71.4 ◯ Example 1-1-4 Comparative CAM20 40 71.5 ◯Example 1-1-5 Comparative CAM20 50 72 ◯ Example 1-1-6 Comparative CAM2060 72.5 ◯ Example 1-1-7 Comparative CAM20 70 72.7 ◯ Example 1-1-8Comparative CAM20 80 73.3 ◯ Example 1-1-9 Comparative CAM20 90 73.8 XExample 1-1-10 Comparative CAM10a 0 80.8 ◯ Example 1-1-11

(1-2) Experimental Example 1-2: Evaluation of life-time and penetrationstability depending on blending ratios of NCM523 (D₅₀: 4.5 μm)

Life-time property and penetration stability of the battery cells havingcompositions as described in Table 3 below were evaluated by methods thesame as those of Experimental Example 1-1.

TABLE 3 Second Lithium Life-Time Metal Oxide Property (D₅₀: 4.5 μm) (500First Lithium Blending Ratio cycle) Penetration Metal Oxide (wt %) (%)Stability Example 1-2-1 CAM10a 10 82.1 ◯ Example 1-2-2 CAM10a 20 82.8 ◯Example 1-2-3 CAM10a 30 84.2 X Example 1-2-4 CAM10a 40 84.8 X Example1-2-5 CAM10a 50 86.3 X Example 1-2-6 CAM10a 60 87 X Example 1-2-7 CAM10a70 87.9 X Example 1-2-8 CAM10a 80 88.8 X Example 1-2-9 CAM10a 90 90.1 XComparative CAM20 10 70.7 ◯ Example 1-2-1 Comparative CAM20 20 70.9 ◯Example 1-2-2 Comparative CAM20 30 71.5 ◯ Example 1-2-3 ComparativeCAM20 40 71.7 ◯ Example 1-2-4 Comparative CAM20 50 72.4 ◯ Example 1-2-5Comparative CAM20 60 72.9 ◯ Example 1-2-6 Comparative CAM20 70 73.3 ◯Example 1-2-7 Comparative CAM20 80 73.6 ◯ Example 1-2-8 ComparativeCAM20 90 74 X Example 1-2-9

(1-3) Experimental Example 1-3: Evaluation of life-time and penetrationstability depending on blending ratios of NCM523 (D₅₀: 7 μm)

Life-time property and penetration stability of the battery cells havingcompositions as described in Table 4 below were evaluated by methods thesame as those of Experimental Example 1-1.

TABLE 4 Second Lithium Metal Oxide (D₅₀: 7 μm) Life-Time BlendingProperty First Lithium Ratio (500 cycle) Penetration Metal Oxide (wt %)(%) Stability Example 1-3-1 CAM10a 10 82.3 ◯ Example 1-3-2 CAM10a 20 83◯ Example 1-3-3 CAM10a 30 84.2 X Example 1-3-4 CAM10a 40 85.5 X Example1-3-5 CAM10a 50 86.7 X Example 1-3-6 CAM10a 60 87 X Example 1-3-7 CAM10a70 88.3 X Example 1-3-8 CAM10a 80 89.5 X Example 1-3-9 CAM10a 90 90.7 XComparative CAM20 10 70.4 ◯ Example 1-3-1 Comparative CAM20 20 71.1 ◯Example 1-3-2 Comparative CAM20 30 71.7 ◯ Example 1-3-3 ComparativeCAM20 40 72 ◯ Example 1-3-4 Comparative CAM20 50 72.8 ◯ Example 1-3-5Comparative CAM20 60 73.1 ◯ Example 1-3-6 Comparative CAM20 70 73.7 ◯Example 1-3-7 Comparative CAM20 80 74.1 X Example 1-3-8 ComparativeCAM20 90 74.4 X Example 1-3-9

(1-4) Experimental Example 1-4: Evaluation of life-time and penetrationstability depending on blending ratios of NCM523 (D₅₀: 10 μm)

Life-time property and penetration stability of the battery cells havingcompositions as described in Table 5 below were evaluated by methods thesame as those of Experimental Example 1-1.

TABLE 5 Second Lithium Metal Oxide (D₅₀: 10 μm) Life-Time BlendingProperty First Lithium Ratio (500 cycle) Penetration Metal Oxide (wt %)(%) Stability Example 1-4-1 CAM10a 10 82.4 ◯ Example 1-4-2 CAM10a 2083.5 ◯ Example 1-4-3 CAM10a 30 84.2 X Example 1-4-4 CAM10a 40 85.3 XExample 1-4-5 CAM10a 50 87 X Example 1-4-6 CAM10a 60 88.1 X Example1-4-7 CAM10a 70 89 X Example 1-4-8 CAM10a 80 90.5 X Example 1-4-9 CAM10a90 91.6 X Comparative CAM20 10 70.7 ◯ Example 1-4-1 Comparative CAM20 2071.1 ◯ Example 1-4-2 Comparative CAM20 30 71.8 ◯ Example 1-4-3Comparative CAM20 40 72 ◯ Example 1-4-4 Comparative CAM20 50 72.8 ◯Example 1-4-5 Comparative CAM20 60 73.1 ◯ Example 1-4-6 ComparativeCAM20 70 74.1 X Example 1-4-7 Comparative CAM20 80 74.5 X Example 1-4-8Comparative CAM20 90 75 X Example 1-4-9

(1-5) Experimental Example 1-5: Evaluation of life-time and penetrationstability depending on blending ratios of NCM523 (D₅₀: 15 μm)

Life-time property and penetration stability of the battery cells havingcompositions as described in Table 6 below were evaluated by methods thesame as those of Experimental Example 1-1.

TABLE 6 Second Lithium Metal Oxide (D₅₀: 15 μm) Life-Time BlendingProperty First Lithium Ratio (500 cycle) Penetration Metal Oxide (wt %)(%) Stability Example 1-5-1 CAM10a 10 82.5 ◯ Example 1-5-2 CAM10a 2083.5 ◯ Example 1-5-3 CAM10a 30 84.4 X Example 1-5-4 CAM10a 40 85.9 XExample 1-5-5 CAM10a 50 87.4 X Example 1-5-6 CAM10a 60 88.1 X Example1-5-7 CAM10a 70 89 X Example 1-5-8 CAM10a 80 90.5 X Example 1-5-9 CAM10a90 92 X Comparative CAM20 10 70.3 ◯ Example 1-5-1 Comparative CAM20 2071.1 ◯ Example 1-5-2 Comparative CAM20 30 71.9 ◯ Example 1-5-3Comparative CAM20 40 72.4 ◯ Example 1-5-4 Comparative CAM20 50 72.9 ◯Example 1-5-5 Comparative CAM20 60 73.7 ◯ Example 1-5-6 ComparativeCAM20 70 74 X Example 1-5-7 Comparative CAM20 80 75.1 X Example 1-5-8Comparative CAM20 90 75.5 X Example 1-5-9

Referring to Tables 2 to 6 above, the batteries of Examples showedimproved life-time property and penetration stability compared to thosein Comparative Examples.

Regarding a particle dimension of the second lithium metal oxide (D₅₀),the life-time property and penetration stability were generally improvedfrom Experimental Example 1-1 to Example 1-5.

In Examples, when the bending ratio of the first lithium metal oxide andthe second lithium metal oxide was from about 50:50 to about 10:90, thepenetration stability was improved in substantially entire region ofD₅₀.

When the particle dimension of the second lithium metal oxide (D₅₀) wasfrom 4.5 μm to 15 μm, the blending ratios of the first lithium metaloxide and the second lithium metal oxide in which the ignition orexplosion by the penetration did not occur were widely expanded.

Experimental Example 2: Blending a first cathode active material havinga FCG structure and a second cathode active material having a fixedconcentration

Fabrication of Lithium Secondary Battery

(1) Cathode

A mixing ratio of precursors was continuously changed to formprecipitates so that a first cathode active material particle having anentire composition of LiNi_(0.8)Co_(0.1)Mn_(0.1)O₂ and having acontinuous concentration gradient from a central composition ofLiNi_(0.84)Co_(0.11)Mn_(0.05)O₂ to a surface composition ofLiNi_(0.78)Co_(0.10)Mn_(0.12)O₂ was formed (hereinafter, referred to asCAM10b and also see an image of FIG. 4). Additionally, a second cathodeactive material particle having uniform concentrations (or molar ratios)of nickel, manganese and cobalt from a central portion to a surface(hereinafter, referred to as NCM523) was prepared.

Blending ratios of the first and second cathode active materialparticles were adjusted as listed in following Tables to form cathodeactive materials. The cathode active material, Denka Black as aconductive additive and PVDF as a binder were mixed by a weight ratio of92:5:3 to form a positive electrode slurry. The positive electrodeslurry was coated, dried, and pressed on an aluminum collector to form acathode. A density of the cathode after the pressing was 3.3 g/cc.

FIG. 3 is a schematic cross-sectional view illustrating positions atwhich a concentration gradient of a first cathode active materialparticle prepared in accordance with some example embodiments ismeasured. Referring to FIG. 3, a distance from the central portion tothe surface of the first cathode active material particle was 5 μm, andthe concentration was measured per a distance of 5/7 μm. The results arelisted in Table 7 below.

TABLE 7 Position Molar Ratio Molar Ratio Molar Ratio Number of Ni of Coof Mn 1 77.97 10.07 11.96 2 80.98 9.73 9.29 3 82.68 10.32 7 4 82.6 107.4 5 82.55 10.37 7.07 6 83.24 10.86 5.9 7 84.33 10.83 4.84

(2) Anode

An anode was fabricated by a method the same as that of ExperimentalExample 1.

(3) Lithium Secondary Battery

A lithium secondary battery was fabricated using the cathode and theanode prepared as described above by a method the same as that ofExperimental Example 1.

Examples and Comparative Examples

Blends of the cathode active material particles CAM10b and NCM523 wereused in Examples. LiNi_(0.8)Co_(0.1)Mn_(0.1)O₂ (hereinafter, referred toas CAM20 and see an image of FIG. 5) having a uniform compositionthroughout an entire region of the particle was used as the cathodeactive material in Comparative Examples.

Methods of forming the cathode, the anode and the lithium secondarybattery were the same in Examples and Comparative Examples except forthe cathode active material particles.

(2-1) Experimental Example 2-1: Evaluation of life-time and penetrationstability depending on blending ratios of NCM523 (D₅₀: 3 μm)

The battery cells prepared as described in Table 8 below were repeatedlycharged (1 C 4.2 V 0.1 C CUT-OFF) and discharged (1 C 3.0 V CUT-OFF) 500times, and then a discharging capacity at a 500th cycle was calculatedas a percentage (%) with respect to a first cycle discharging capacityto measure the life-time property.

Additionally, the battery cells of Example and Comparative Examples werecharged (1C 4.2V 0.1C CUT-OFF), and then the battery cells werepenetrated by a nail having a diameter of 3 mm at a speed of 80 mm/secto check whether ignition or explosion occurred (O: Ignition orexplosion occurred, X: No ignition or explosion).

The results are shown in Table 8 below.

TABLE 8 Second Cathode Active Material Particle First D₅₀ (3 μm) CathodeNCM523 Life-Time Active Blending Property Material Ratio (500 cycle)Penetration Particle (wt %) (%) Stability Example 2-1-1 CAM10b 10 83.1 ◯Example 2-1-2 CAM10b 20 84 ◯ Example 2-1-3 CAM10b 30 84.8 ◯ Example2-1-4 CAM10b 40 86.3 ◯ Example 2-1-5 CAM10b 50 87.2 X Example 2-1-6CAM10b 60 87.9 X Example 2-1-7 CAM10b 70 89.1 X Example 2-1-8 CAM10b 8089.9 X Example 2-1-9 CAM10b 90 91 X Comparative CAM10b 0 81.8 ◯ Example2-1-1 Comparative CAM20 0 69.8 ◯ Example 2-1-2 Comparative CAM20 10 70.5◯ Example 2-1-3 Comparative CAM20 20 70.7 ◯ Example 2-1-4 ComparativeCAM20 30 71.4 ◯ Example 2-1-5 Comparative CAM20 40 71.5 ◯ Example 2-1-6Comparative CAM20 50 72 ◯ Example 2-1-7 Comparative CAM20 60 72.5 ◯Example 2-1-8 Comparative CAM20 70 72.7 ◯ Example 2-1-9 ComparativeCAM20 80 73.3 ◯ Example 2-1-10 Comparative CAM20 90 73.8 X Example2-1-11

(2-2) Experimental Example 2-2: Evaluation of life-time and penetrationstability depending on blending ratios of NCM523 (D₅₀: 4.5 μm)

Life-time property and penetration stability of the battery cells havingcompositions as described in Table 9 below were evaluated by methods thesame as those of Experimental Example 2-1.

TABLE 9 Second Cathode Active Material Particle First D₅₀ (4.5 μm)Cathode NCM523 Life-Time Active Blending Property Material Ratio (500cycle) Penetration Particle (wt %) (%) Stability Example 2-2-1 CAM10b 1082.9 ◯ Example 2-2-2 CAM10b 20 84.4 ◯ Example 2-2-3 CAM10b 30 85 XExample 2-2-4 CAM10b 40 86.3 X Example 2-2-5 CAM10b 50 87.5 X Example2-2-6 CAM10b 60 88.4 X Example 2-2-7 CAM10b 70 89.9 X Example 2-2-8CAM10b 80 90.9 X Example 2-2-9 CAM10b 90 91.7 X Comparative CAM10b 082.1 ◯ Example 2-2-1 Comparative CAM20 0 69.8 ◯ Example 2-2-2Comparative CAM20 10 70.7 ◯ Example 2-2-3 Comparative CAM20 20 70.9 ◯Example 2-2-4 Comparative CAM20 30 71.5 ◯ Example 2-2-5 ComparativeCAM20 40 71.7 ◯ Example 2-2-6 Comparative CAM20 50 72.4 ◯ Example 2-2-7Comparative CAM20 60 72.9 ◯ Example 2-2-8 Comparative CAM20 70 73.3 ◯Example 2-2-9 Comparative CAM20 80 73.6 ◯ Example 2-2-10 ComparativeCAM20 90 74 X Example 2-2-11

(2-3) Experimental Example 2-3: Evaluation of life-time and penetrationstability depending on blending ratios of NCM523 (D₅₀: 7 μm)

Life-time property and penetration stability of the battery cells havingcompositions as described in Table 10 below were evaluated by methodsthe same as those of Experimental Example 2-1.

TABLE 10 Second Cathode Active Material Particle First D₅₀ (7 μm)Cathode NCM523 Life-Time Active Blending Property Material Ratio (500cycle) Penetration Particle (wt %) (%) Stability Example 2-3-1 CAM10b 1083.3 ◯ Example 2-3-2 CAM10b 20 84.5 ◯ Example 2-3-3 CAM10b 30 85.2 XExample 2-3-4 CAM10b 40 86.7 X Example 2-3-5 CAM10b 50 87.6 X Example2-3-6 CAM10b 60 88.9 X Example 2-3-7 CAM10b 70 90.3 X Example 2-3-8CAM10b 80 91.1 X Example 2-3-9 CAM10b 90 92.2 X Comparative CAM10b 082.2 ◯ Example 2-3-1 Comparative CAM20 0 69.8 ◯ Example 2-3-2Comparative CAM20 10 70.4 ◯ Example 2-3-3 Comparative CAM20 20 71.1 ◯Example 2-3-4 Comparative CAM20 30 71.7 ◯ Example 2-3-5 ComparativeCAM20 40 72 ◯ Example 2-3-6 Comparative CAM20 50 72.8 ◯ Example 2-3-7Comparative CAM20 60 73.1 ◯ Example 2-3-8 Comparative CAM20 70 73.7 ◯Example 2-3-9 Comparative CAM20 80 74.1 X Example 2-3-10 ComparativeCAM20 90 74.4 X Example 2-3-11

(2-4) Experimental Example 2-4: Evaluation of life-time and penetrationstability depending on blending ratios of NCM523 (D₅₀: 10 μm)

Life-time property and penetration stability of the battery cells havingcompositions as described in Table 11 below were evaluated by methodsthe same as those of Experimental Example 2-1.

TABLE 11 Second Cathode Active Material Particle First D₅₀ (10 μm)Cathode NCM523 Life-Time Active Blending Property Material Ratio (500cycle) Penetration Particle (wt %) (%) Stability Example 2-4-1 CAM10b 1083.1 ◯ Example 2-4-2 CAM10b 20 84.4 ◯ Example 2-4-3 CAM10b 30 85.7 XExample 2-4-4 CAM10b 40 86.9 X Example 2-4-5 CAM10b 50 88.2 X Example2-4-6 CAM10b 60 89.6 X Example 2-4-7 CAM10b 70 90.6 X Example 2-4-8CAM10b 80 92.1 X Example 2-4-9 CAM10b 90 93.4 X Comparative CAM10b 081.8 ◯ Example 2-4-1 Comparative CAM20 0 69.8 ◯ Example 2-4-2Comparative CAM20 10 70.7 ◯ Example 2-4-3 Comparative CAM20 20 71.1 ◯Example 2-4-4 Comparative CAM20 30 71.8 ◯ Example 2-4-5 ComparativeCAM20 40 72 ◯ Example 2-4-6 Comparative CAM20 50 72.8 ◯ Example 2-4-7Comparative CAM20 60 73.1 ◯ Example 2-4-8 Comparative CAM20 70 74.1 XExample 2-4-9 Comparative CAM20 80 74.5 X Example 2-4-10 ComparativeCAM20 90 75 X Example 2-4-11

(2-5) Experimental Example 2-5: Evaluation of life-time and penetrationstability depending on blending ratios of NCM523 (D₅₀: 15 μm)

Life-time property and penetration stability of the battery cells havingcompositions as described in Table 12 below were evaluated by methodsthe same as those of Experimental Example 2-1.

TABLE 12 Second Cathode Active Material Particle First D₅₀ (15 μm)Cathode NCM523 Life-Time Active Blending Property Material Ratio (500cycle) Penetration Particle (wt %) (%) Stability Example 2-5-1 CAM10b 1083.1 ◯ Example 2-5-2 CAM10b 20 84.7 ◯ Example 2-5-3 CAM10b 30 86 XExample 2-5-4 CAM10b 40 87.3 X Example 2-5-5 CAM10b 50 88.6 X Example2-5-6 CAM10b 60 89.6 X Example 2-5-7 CAM10b 70 91 X Example 2-5-8 CAM10b80 92.3 X Example 2-5-9 CAM10b 90 93.8 X Comparative CAM10b 0 81.9 ◯Example 2-5-1 Comparative CAM20 0 69.8 ◯ Example 2-5-2 Comparative CAM2010 70.3 ◯ Example 2-5-3 Comparative CAM20 20 71.1 ◯ Example 2-5-4Comparative CAM20 30 71.9 ◯ Example 2-5-5 Comparative CAM20 40 72.4 ◯Example 2-5-6 Comparative CAM20 50 72.9 ◯ Example 2-5-7 ComparativeCAM20 60 73.7 ◯ Example 2-5-8 Comparative CAM20 70 74 X Example 2-5-9Comparative CAM20 80 75.1 X Example 2-5-10 Comparative CAM20 90 75.5 XExample 2-5-11

Referring to Tables 8 to 12 above, the batteries of Examples usingblends of the first cathode active material particle having theconcentration gradient (CAM10b) and the second cathode active materialparticle of a fixed composition (NCM523) showed improved life-timeproperty and penetration stability compared to those in ComparativeExamples.

The battery cells of Comparative Examples showed generally degradedlife-time property and penetration stability, and the ignition did notoccur only when an excess of NCM523 was included.

In Examples 2-1 to 2-5, when the bending ratio of the first cathodeactive material particle and the second cathode active material particlewas from about 50:40 to about 10:90, the ignition or explosion by thepenetration did not occur.

When the particle dimension (D₅₀) of the second lithium metal oxide(NCM523) was from 4.5 μm to 15 μm, the blending ratios of the firstcathode active material particle and the second cathode active materialparticle in which the ignition or explosion by the penetration did notoccur were widely expanded.

What is claimed is:
 1. A lithium secondary battery, comprising: acathode formed from a cathode active material including a first cathodeactive material particle and a second cathode active material particle;an anode; and a separator interposed between the cathode and the anode,wherein the first cathode active material particle includes a lithiummetal oxide including a continuous concentration gradient in at leastone region between a central portion and a surface portion, wherein thesecond cathode active material particle includes a lithium metal oxideincluding at least two metals except for lithium which have constantconcentrations from a central portion to a surface portion, and thesecond cathode active material particle includes an excess amount ofnickel among the metals except for lithium, wherein the first cathodeactive material particle includes a first metal having a continuouslydecreasing concentration between the central portion and the surfaceportion, and a second metal having a continuously increasingconcentration between the central portion and the surface portion, andwherein the central portion of the first cathode active materialparticle is a central point of the first cathode active materialparticle or a region within a predetermined diameter from the centralpoint, and the surface portion of the first cathode active materialparticle is an outermost surface of the first cathode active materialparticle or a region that is a predetermined thickness from theoutermost surface.
 2. The lithium secondary battery according to claim1, wherein the first cathode active material particle further includes athird metal having a constant concentration from the central portion tothe surface portion.
 3. The lithium secondary battery according to claim2, wherein the first cathode active material particle is represented bythe following Chemical Formula 1:Li_(x)M1_(a)M2_(b)M3_(c)O_(y)  [Chemical Formula 1 ] wherein, in theChemical Formula 1 above, M 1, M2 and M3 each represents the firstmetal, the second metal and the third metal, and are selected from Ni,Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al,Ga or B, and 0<x≤1.1, 2≤y≤2.02, 0<a<1, 0<b<1, 0<c<1, and 0<a+b+c≤1. 4.The lithium secondary battery according to claim 3, wherein 0.6≤a ≤0.95and 0.05≤b+c≤0.4 in the Chemical Formula
 1. 5. The lithium secondarybattery according to claim 3, wherein 0.7≤a ≤0.9 and 0.1≤b+c≤0.3 in theChemical Formula
 1. 6. The lithium secondary battery according to claim3, wherein the first metal is nickel (Ni), the second metal is manganese(Mn) and the third metal is cobalt (Co).
 7. The lithium secondarybattery according to claim 1, wherein the first cathode active materialparticle includes a concentration gradient layer formed between thecentral portion and the surface portion, wherein the central portion ofthe first cathode active material particle is a region within apredetermined diameter from the central point, and the surface portionof the first cathode active material particle is a region that is apredetermined thickness from the outermost surface.
 8. The lithiumsecondary battery according to claim 7, wherein the concentrationgradient layer includes a continuous concentration gradient, wherein thecentral portion and the surface portion each has a constantconcentration composition, and the central portion and the surfaceportion have different concentration compositions from each otherthrough the concentration gradient layer.
 9. The lithium secondarybattery according to claim 1, wherein the first cathode active materialparticle has the continuous concentration gradient throughout an entireregion from the central point of the first cathode active materialparticle to the outermost surface thereof.
 10. The lithium secondarybattery according to claim 1, wherein the second cathode active materialparticle is represented by the following Chemical Formula 2:Li_(x)M1′_(a)M2′_(b)M3′_(c)O_(y)  [Chemical Formula 2 ] wherein, in theChemical Formula 2 above, M1′ is nickel, and M2′ and M3′ are selectedfrom Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo,Al, Ga, W or B, and 0<x≤1.1, 2≤y≤2.02, 0<a+b+c≤1, 0.48≤a≤0.520.18≤b≤0.22 and 0.28≤c ≤0.32.
 11. The lithium secondary batteryaccording to claim 10, wherein 0.49≤a≤0.51, 0.19≤b≤0.21 and 0.29≤c≤0.31in the Chemical Formula
 2. 12. The lithium secondary battery accordingto claim 10, wherein M2′ and M3′ are cobalt (Co) and manganese (Mn),respectively.
 13. The lithium secondary battery according to claim 12,wherein a molar ratio of nickel, cobalt and manganese in the secondcathode active material particle is 5:2:3.
 14. The lithium secondarybattery according to claim 1, wherein a blending ratio of the firstcathode active material particle and the second cathode active materialparticle is in a range from 7:3 to 1:9.
 15. The lithium secondarybattery according to claim 1, wherein a blending ratio of the firstcathode active material particle and the second cathode active materialparticle is in a range from 5:5 to 1:9.
 16. The lithium secondarybattery according to claim 1, wherein an average diameter (D₅₀) of thesecond cathode active material particle is in a range from 3 μm to 15μm.
 17. The lithium secondary battery according to claim 1, an averagediameter (D₅₀) of the second cathode active material particle is in arange from 4.5 μm to 15 μm.